The present invention relates to an intracranial pressure relief valve and, more particularly, to a single piece combination valve stem and fluid flow restrictor for use in a three stage valve of the type which provides either constant pressure or constant flow characteristics in accordance with a fluid pressure differential applied across the valve.
Hydrocephalus is a condition in which the body, for any one of a variety of reasons, is unable to relieve itself of excess cerebrospinal fluid (CSF) collected in the ventricles of the brain. The excessive collection of CSF in the ventricles results in an abnormal increase in both epidural and intradural pressures. This in turn causes a number of adverse physiological effects including compression of brain tissue, impairment of blood flow in the brain tissue and impairment of the brain's normal metabolism.
Treatment of a hydrocephalic condition frequently involves relieving the abnormally high intracranial pressure. Accordingly, a variety of CSF pressure regulator valves and methods of controlling CSF pressur have been developed which include various check valves, servo valves or combinations thereof. Generally, such valves serve to divert CSF from the ventricles of the brain through a discharge line to some suitable drainage location in the body such as the venous system or the peritoneal cavity. Check valves operate by opening when the difference between CSF pressure and pressure in the discharge line exceeds a predetermined value.
The use of a simple check valve in the treatment of hydrocephalus is potentially disadventageous since it is possible for such a valve to open in response to a sudden, but nevertheless perfectly normal, increase in differential pressure between CSF in the ventricular spaces and fluid at the selected discharge location of the body, resulting in abnormal and potentially dangerous hyperdrainage of the ventricular spaces. For example, when a patient stands after lying in a recumbent position, the resulting increased vertical height of the fluid column existing between the head and the selected drainage location may result in such an increase in differential pressure. Accordingly, valves, such as that described in the copending application of the present inventor, Ser. No. 559,392, filed Dec. 8, 1983, have been developed which serve to prevent undesired hyperdrainage by limiting the flow rate of fluid through the valve when a sudden increase in differential pressure occurs.
In this valve, a diaphragm, movable in response to the pressure differential between ventricular CSF pressure and pressure of fluids at the drainage location of the body, was mechanically coupled to a valve seat having a fluid metering orifice extending therethrough. The orifice allowed passage of CSF from the ventricular spaces to the selected drainage location. Motion of the diaphragm in response to changes in the differential pressure caused the valve seat to be moved from a first position, in which the valve seat contacted a suitably located sphere to block and thereby prevent the passage of fluid through the orifice, to a second position, in which a generally cylindrical fluid flow restrictor partially occluded the orifice, thereby limiting fluid flow therethrough. By controlling the position of the sphere, the valve seat and the restrictor, it was possible to construct a valve having flow characteristics which avoided hyperdrainage with sudden changes in differential pressure.
In order to assure optimum performance of such a valve, it was necessary to carefully control the dimensions of the sphere, the valve seat, the orifice and the restrictor. Since the parts involved were quite small, and involved working tolerances on the order of 0.0001 inch, considerable manufacturing costs were incurred in constructing such a valve.
The present invention is directed to an improvement in such a valve wherein the number of manufacturing steps, and hence the cost of the valve, is reduced. Basically, a valve constructed in accordance with the present invention is provided with a one-piece member which replaces both the sphere and the flow restrictor. Since the one-piece member does not include spherical surfaces, the difficulties associated with machining such a surface are avoided.
In view of the foregoing, it is a general object of the present invention to provide a new and improved pressure regulator valve for relieving intracranial pressure caused by the presence of excess CSF in the ventricles of the brain.
It is a more specific object of the present invention to provide a pressure regulator valve which includes components which may be easily and economically manufactured.
It is a still more specific object of the present invention to provide a pressure regulator valve in which critically dimensioned components are of an easily manufactured configuration.